The present invention relates to a method and apparatus for manufacturing a substrate, and more particularly to a method and apparatus for manufacturing a substrate which reliably supplies a conductive ball to a plurality of pads of the substrate.
For example, in a wiring board of a BGA (Ball Grid Array) type or a flip-chip type, a flux is applied to pads arranged at a predetermined interval and a conductive ball is then supplied onto the flux, and a solder bump is formed on the pad through a reflow.
In a manufacturing line for the wiring board, moreover, a diameter of a conductive ball and a pitch of an interval are reduced with a reduction in a size of a semiconductor chip. For this reason, it is desirable to arrange a large number of conductive balls in all pads accurately and efficiently.
For example, a conventional conductive ball supplying method includes a transfer method of mounting, on a substrate, a mask (a conductive ball supplying member) having a plurality of holes arranged at an equal pitch to that of the pads and supplying a large number of conductive balls onto the mask, and dropping the conductive balls one by one into each of the holes of the mask (for example, see Patent Documents 1 and 2) and an adsorbing and loading method of adsorbing a conductive ball into each hole of a mask by means of an adsorbing jig to which a mask is attached and moving the adsorbing jig onto a substrate, thereby supplying the conductive ball to a pad on the substrate through a release of the adsorption (for example, see Patent Document 3).
In the method using the mask, thus, the conductive balls are supplied in a lump to a plurality of wiring boards in a state of a large substrate in which a plurality of wiring boards has not been divided into pieces in order to enhance a production efficiency.
Description will be given to a manufacturing method using the conventional transfer method. FIG. 1A is a plan view showing a multi-unit substrate. FIG. 1B is a plan view showing a mask corresponding to the multi-unit substrate. FIG. 1C is a longitudinal sectional view showing the case in which an alignment of a hole of the mask and that of a pad of the substrate are coincident with each other. FIG. 1D is a longitudinal sectional view showing the case in which the alignment of the hole of the mask and that of the pad of the substrate are not coincident with each other.
As shown in FIG. 1A, a multi-unit substrate 10 has a plurality of wiring boards 20 (201 to 20n) arranged in X and Y directions, and each of the wiring boards 20 has a plurality of pads 30 (301 to 30n) arranged to be exposed at a certain pitch (interval) in the X and Y directions. For convenience of explanation, a boundary line is shown in FIG. 1A in order to cause a region of the wiring board 20 to be clear. However, the boundary line is not actually present.
As shown in FIG. 1B, a mask (a conductive ball supplying member) 40 is formed to have a larger dimension in the X and Y directions than the dimension of the substrate 10, and a plurality of conductive ball inserting holes 50 (501 to 50n) at an equal pitch to the pads 30 (301 to 30n) is provided every region corresponding to the wiring boards 20 (201 to 20n). Moreover, the conductive ball inserting hole 50 (501 to 50n) is provided to have a slightly larger diameter than the diameter of the pad 30 (301 to 30n).
The mask 40 is formed by a thin metal plate having a magnetic property, for example, and is delivered to an opposed position to an upper surface of the substrate 10 and positions in the X and Y directions with respect to the substrate 10 are adjusted, and the mask 40 is thus mounted on the upper surface of the substrate 10.
As shown in FIG. 1C, the mask 40 is adjusted and fixed into a position in which the conductive ball inserting hole 50 (501 to 50n) is coincident with the pad 30 (301 to 30n). For a method of fixing the mask 40, for example, there is used a method of disposing a permanent magnet or an electromagnet on a lower surface side of the substrate 10 and adsorbing the mask 40 by a magnetic force, and fixing the mask 40 onto the upper surface of the substrate 10 in the case in which the mask 40 is formed by a magnetic material.
The position of the mask 40 with respect to the substrate 10 is adjusted in such a manner that the conductive ball inserting hole 50 (501 to 50n) is coincident with the pad 30 (301 to 30n) and a large number of conductive balls 60 are then supplied and are transferred into the conductive ball inserting holes 50 (501 to 50n). A flux is applied to a surface of the pad 30 (301 to 30n). Therefore, the conductive ball 60 taking a spherical shape inserted in the conductive ball inserting hole 50 (501 to 50n) is stuck to the flux having an adhesiveness. Then, a reflow is carried out to fuse the conductive ball 60, thereby forming a solder bump connected to the pad 30 (301 to 30n)
[Patent Document 1] JP-A-2006-005276
[Patent Document 2] JP-A-09-162533
[Patent Document 3] JP-A-2003-100789
In the substrate 10, however, an insulating layer and a conductive layer are laminated through various steps. For this reason, the position of the pad 30 (301 to 30n) is moved forward and backward in the X and Y directions in a process for carrying out a processing of each step. For example, as shown in FIG. 1B, there will be considered a division into regions A1 to A5 in which the conductive ball inserting hole 50 (501 to 50n) of the mask 40 is provided. In the region A3 on a center of the mask, the conductive ball inserting hole 50 (501 to 50n) is coincident with the pad 30 (301 to 30n). Therefore, the conductive ball 60 can be supplied to the pad 30 (301 to 30n). In the regions A2 and A4 positioned on an outside of the region A3, moreover, the conducive ball inserting hole 50 (501 to 50n) and the pad 30 (301 to 30n) are slightly shifted from each other and a part of the pad 30 (301 to 30n) is coincident with the conductive ball inserting hole 50 (501 to 50n). Therefore, the conductive ball 60 can be supplied to the pad 30 (301 to 30n)
In the regions A1 and A5 provided in the vicinity of a peripheral edge portion of the mask 40, however, the conductive ball inserting hole 50 (501 to 50n) and the pad 30 (301 to 30n) are perfectly shifted from each other. Therefore, the conductive ball 60 inserted in the conductive ball inserting hole 50 (501 to 50n) is loaded onto the insulating layer of the substrate 10 which is provided out of the pad 30 (301 to 30n) as shown in FIG. 1D. Consequently, it is impossible to form a solder bump on the pad 30 (301 to 30n).
In the conventional manufacturing method, thus, there is a problem in that a region in which the conductive ball 60 cannot be supplied to the pad 30 is generated in the case in which the position of the pad 30 (301 to 30n) is greatly shifted from the conductive ball inserting hole 50 (501 to 50n) of the mask 40 through the regions A1 to A5 provided on the substrate 10. A relative positional shift tendency of the conductive ball insertion hole 50 (501 to 50n) and the pad 30 (301 to 30n) in each of the regions A1 to A5 shown in FIG. 1B is not necessarily determined but the influence of the expansion and contraction of the substrate 10 is shown for easy understanding.
Moreover, the expansion and contraction of the substrate rarely appears uniformly. In many cases, therefore, the substrate is almost expanded and contracted to be laterally asymmetrical. In some cases, moreover, the substrate is expanded and contracted in a different direction every lot. As a countermeasure to be taken against the positional shift of the pad 30 through the expansion and contraction of the substrate, it is possible to propose a method of measuring a direction and amount of the expansion and contraction every lot and preparing the mask 40 in which the conductive ball inserting hole 50 is formed in a corresponding position to a result of the measurement. In the method, however, there is fabricated the mask 40 which is varied every lot. For this reason, it is hard to execute the method.